Sensor controller

ABSTRACT

A sensor controller for a particulate matter detection sensor includes a signal output circuit connected to the particulate matter detection sensor such that a sensor detection value is changeable in a predetermined output range by the signal output circuit, a heater configured to heat an attachment portion so as to burn and remove particulate matter attached to the attachment portion, a learning portion for calculating a sensor standard value in a state where the resistance between a pair of opposed electrodes is reduced based on an obtained sensor detection value and for storing the sensor standard value as a learning value, and a correcting portion for correcting the sensor detection value based on the sensor standard value stored by the learning portion.

CROSS REFERENCE TO RELATED APPLICATION

This application is based on Japanese Patent Application No. 2010-177512filed on Aug. 6, 2010, the contents of which are incorporated herein byreference in its entirety.

TECHNICAL FIELD

The present invention relates to a sensor controller for calculating anamount of particulate matter (PM) based on a detection signal from aparticulate matter detection sensor.

BACKGROUND

Various types of PM sensors (particulate matter detection sensors) fordetecting the amount of PM exhausted from an engine or the like havebeen proposed. For example, a PM sensor disclosed in JP 59-196453A(corresponding to U.S. Pat. No. 4,656,832) includes a pair of opposedelectrodes on an insulating substrate. The accumulation of PM changes aresistance between the pair of the electrodes. By using this property,the PM sensor is configured to detect the amount of PM by measuring theresistance between the electrodes. In this case, a detection circuitconnected to a sensor element forms a voltage-dividing circuitconfigured by a resistance between the pair of opposed electrodes and apredetermined shunt resistance. The detection circuit is configured tooutput a voltage at an intermediate point of the voltage-dividingcircuit as a sensor detected signal.

However, in the PM sensor and the detection circuit, a sensordifference, a variation in an elapsed time, a circuit error or the likemay be caused, and thereby the PM amount may be incorrectly detected.For example, if a foreign matter such as a metal piece is attached to aninsulating substrate of the PM sensor, or if a weak leakage currentflows with the impurities in the insulating substrate, a sensor outputwhich originally should not be produced may be caused, or the sensoroutput may become larger than a value originally assumed.

In view of the foregoing problems, it is an object of the presentinvention to provide a sensor controller which can effectively reduce adetection error of a particulate matter detection sensor (PM sensor) andcan accurately detect the amount of particulate matter.

According to an aspect of the present invention, a sensor controller isadapted to a particulate matter detection sensor. The particulate matterdetection sensor includes an attachment portion to which conductiveparticulate matter contained in gas is attached, and a pair of opposedelectrodes spaced from each other at the attachment portion.Furthermore, the particulate matter detection sensor is adapted tooutput a detection signal corresponding to a resistance between the pairof opposed electrodes. The sensor controller is adapted to calculate anamount of attached particulate matter based on a sensor detection valuefrom the particulate matter detection sensor. The sensor controllerincludes: a signal output circuit (e.g., voltage-dividing circuit)connected to the particulate matter detection sensor such that thesensor detection value is changeable in a predetermined output range bythe signal output circuit; a heater configured to heat the attachmentportion so as to burn and remove the particulate matter attached to theattachment portion; learning means for obtaining the sensor detectionvalue in a burning of the particulate matter by using heat of theheater, for calculating a sensor standard value in a state where theresistance between the pair of opposed electrodes is reduced based onthe obtained sensor detection value, and for storing the sensor standardvalue as a learning value; and correcting means for correcting thesensor detection value based on the sensor standard value stored by thelearning means. Here, the heater may include a heating unit for burningand removing the particulate mater by using the heat generated from theheater unit, and a heating means for heating the exhaust gas to aburning temperature of the particulate matter, and the like.

Thus, even when the sensor standard value does not become a limit valuein the predetermined output range, an error of the particulate matterdetection sensor can be determined, and the sensor detection value canbe accurately corrected. As a result, a detection error of a particulatematter detection sensor (PM sensor) can be effectively reduced, andthereby the amount of particulate matter can be accurately detected.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects, features and advantages of the present invention willbecome more apparent from the following description made with referenceto the accompanying drawings, in which like parts are designated by likereference numbers and in which:

FIG. 1 is a schematic configuration diagram showing the outline of anengine control system according to an embodiment of the invention;

FIG. 2 is an exploded perspective view showing a main structure of asensor element in a PM sensor;

FIG. 3 is an electric configuration diagram regarding the PM sensor;

FIG. 4 is a flow diagram showing an output error learning process;

FIG. 5 is a timechart for explaining the output error learning process;

FIGS. 6A and 6B are graphs showing sensor output corrections by using azero-point learning value; and

FIGS. 7A and 7B are graphs showing sensor output corrections by using anupper-limit learning value.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, an embodiment of the present invention will be described onthe basis of the drawings. In this embodiment, a vehicle engine systemwith a vehicle-mounted engine is provided to monitor the amount of PM(conductive particulate matter) of exhaust gas exhausted from an engine.In particular, a PM sensor is provided in an engine exhaust pipe. Basedon the amount of attached PM detected by the PM sensor, the amount of PMis monitored. FIG. 1 shows a Configuration diagram of the outline of thesystem.

In FIG. 1, an engine 11 is a direct-injection gasoline engine. Theengine 11 is provided with a fuel injection valve 12 and an igniter 13which serve as an actuator for the operation of the engine 11. Anexhaust pipe 14 of the engine 11 is provided with a three way catalyst15 serving as an exhaust emission control system. An A/F sensor 16 isprovided at an upstream side of the three way catalyst 15, and a PMsensor 17 as a particulate matter detection sensor is provided at adownstream side of the three way catalyst 15. The system is furtherprovided with a rotation sensor 18 for detecting an engine rotationalspeed, a pressure sensor 19 for detecting the pressure of an intakepipe, and the like.

An ECU 20 mainly includes a microcomputer constructed of a well-knownCPU, ROM, RAM, and the like. The ECU executes various control programsstored in the ROM to perform various control processes of the engine 11,based on the operating state of the engine. That is, the ECU 20 receivesinput of respective signals from the above sensors or the like, andcontrols the driving of the fuel injection valve 12 and the igniter 13by computing the amount of injected fuel or the ignition timing based onthe respective signals received.

The ECU 20 calculates the amount of PM actually exhausted from theengine 11 (actual PM emission amount) based on a detection signal fromthe PM sensor 17, and makes a diagnosis of the combustion state of theengine 11 based on the actual PM emission amount. Specifically, when theactual PM emission amount exceeds a predetermined value fordetermination of abnormality, it is determined that the amount ofexhausted PM is excessive and that the engine becomes abnormal.

Further, the ECU 20 may variably control the control state of the engine11 based on the actual PM emission amount calculated from the detectionresult of the PM sensor 17. For example, the ECU 20 can control theamount of injected fuel, the injection timing of fuel, and the ignitiontiming, based on the actual PM emission amount.

Next, the structure of the PM sensor 17, and the electric configurationof the PM sensor 17 will be described using FIGS. 2 and 3. FIG. 2 showsan exploded perspective view of the main structure of a sensor element31 configured in the PM sensor 17, and FIG. 3 shows an electricconfiguration diagram regarding the PM sensor 17.

As shown in FIG. 2, the sensor element 31 includes two pieces ofinsulating substrates 32 and 33 having a longitudinal plate shape. Oneinsulating substrate 32 is provided with a PM detector 34 for detectingthe amount of PM. The other insulating substrate 33 is provided with aheater 35 for heating the sensor element 31. The sensor element 31 is alamination structure in which two layers of the insulating substrates 32and 33 are stacked with each other. The insulating substrate 32corresponds to an attachment portion to which the particulate matter isattached and accumulated.

A pair of detection electrodes 36 a and 36 b are provided on the surfaceof the insulating substrate 32 opposite to the other insulatingsubstrate 33, while being spaced apart from each other. The PM detector34 is made of the pair of the detection electrodes 36 a and 36 b. Eachof the detection electrodes 36 a and 36 b has a comb-like shape withteeth. The teeth of the combs of the detection electrodes 36 a and 36 bare alternatively arranged to be opposite to each other at predeterminedintervals. The heater 35 includes a heating element made of, forexample, an electrically-heated wire.

The shape of the pair of the detection electrodes 36 a and 36 b is notlimited to the above-mentioned one, and may be a curved one.Alternatively, the detection electrodes 36 a and 36 b may be formed froma pair of electrode portions each of which is formed of one wire andwhich are arranged opposed to each other in parallel, while being spacedfrom each other by a predetermined distance.

Although not shown, the PM sensor 17 includes a holder for holding thesensor element 31. The sensor element 31 is fixed to an exhaust pipewith its one end held by the holder. In this case, a part including atleast the PM detector 34 and the heater 35 is positioned in the exhaustpipe, while the PM sensor 17 is attached to the exhaust pipe with theinsulating substrate 32 (PM attachment portion) of the sensor element 31directed toward the upstream side of the exhaust gas. Thus, when exhaustgas containing PM flows through the exhaust pipe, the PM is attached andaccumulated onto the detection electrodes 36 a and 36 b and itssurroundings over the insulating substrate 32. The PM sensor 17 has aprotective cover for covering protrusion parts of the sensor element 31.

When PM in the exhaust gas is attached and accumulated onto theinsulating substrate 32 of the sensor element 31, the PM sensor 17 withthe above structure detects the amount of PM using a change inresistance of the PM detector 34 (that is, resistance between the pairof detection electrodes 36 a and 36 b) which correspond to the amount ofaccumulated PM.

As shown in FIG. 3, the PM sensor 17 has the following electricconfiguration. That is, the PM detector 34 of the PM sensor 17 has oneend thereof connected to a sensor power supply 41, and the other endthereof connected to a shunt resistor 42. The sensor power supply 41 isconstructed of, for example, a constant-voltage circuit. The constantvoltage Vcc is 5 V, for example. In this case, the PM detector 34 andthe shunt resistor 42 form a voltage-dividing circuit 40, in which avoltage of an intermediate point is input as a PM detection voltage Vpm(sensor detection value) to the ECU 20. That is, in the PM detector 34,the resistance Rpm changes according to the amount of accumulated PM.The PM detection voltage Vpm is changed by the resistance Rpm and theresistance Rs of the shunt resistor 42. Then, the PM detection voltageVpm is input to a microcomputer 44 via an A/D converter 43.

When Vcc=5 V and when Rs=5 kΩ, the PM detection voltage Vpm can bedetermined by the following formula (1):Vpm=5 V×5 kΩ/(5 kΩ+Rpm)  (1)

At this time, when the amount of accumulated PM is 0 (or about 0), theresistance Rpm of the PM detector 34 becomes infinite, thereby resultingin Vpm=0 V. When the resistance Rpm of the PM detector 34 decreases, forexample, decreases to 1 kΩ due to the accumulation of PM in the PMdetector 34, the PM detection voltage Vpm becomes in Vpm=4.16V. In thisway, the PM detection voltage Vpm changes according to the amount ofaccumulated PM at the PM detector 34. The microcomputer 44 calculatesthe amount of accumulated PM according to the PM detection voltage Vpm.

The voltage-dividing circuit 40 forms the signal output circuit. The PMdetection voltage Vpm is variably changed by the voltage-dividingcircuit 40 in an output range of 0 to 5 V. In this case, the outputupper limit of the PM detection voltage Vpm is about 5 V, and strictly,slightly lower than 5 V, namely, 4.95V.

In this embodiment, particularly, when the PM is accumulated on the PMdetector 34 as mentioned above, for example, when the resistance Rpm ofthe PM detector 34 becomes 1 kΩ, the PM detection voltage Vpm is “4.16V”, which is small as compared to the output upper limit (5V) of the PMdetection voltage Vpm. This is because an increase in the PM detectionvoltage Vpm is taken into consideration during the forcible burning ofthe PM. The details thereof will be described later. The range of changein the PM detection voltage Vpm during the PM forcible burning is 4.16to 5 V.

The heater 35 of the PM sensor 17 is connected to a heater power supply45. The heater power supply 45 is, for example, a vehicle-mountedbattery. The heater 35 is heated by power supplied from thevehicle-mounted battery. In this case, a transistor 46 is connected as aswitching element to the lower side of the heater 35. The heatingoperation of the heater 35 is controlled by turning on/off thetransistor 46 via the microcomputer 44.

When the energization of the heater 35 is started with the PMaccumulated on the insulating substrate 32, the temperature of theaccumulated PM increases, thereby forcedly burning the accumulated PM.Such forcible burning of the PM burns and removes the PM accumulated onthe insulating substrate 32. For example, at the start of the engine, atthe end of the operation of the engine, or when the amount ofaccumulated PM is determined to reach a predetermined amount, themicrocomputer 44 determines that a request for forcible burning of thePM is made, and thus controls the heating operation of the heater 35.

Further, the ECU 20 is provided with an EEPROM 47 serving as a memoryfor a backup to store therein various types of studied values,abnormality diagnosis values (diagnostic data, or diagdata) or the like.

However, in the PM sensor 17, a sensor difference, a variation in anelapsed time, a circuit error or the like may be caused, and thereby thesensor output may be incorrectly detected. For example, if a foreignmatter such as a metal piece or the like is attached to the insulatingsubstrate 32 of the PM sensor 17, or if a weak leakage current flowswith the impurities in the insulating substrate 32, a sensor outputwhich originally should not be produced may be caused, or the sensoroutput may become larger than a predetermined value originally assumed.

Alternatively, the sensor output may be smaller than the predeterminedvalue originally assumed.

In the present embodiment, the learning of the sensor output error isperformed, and the sensor output is corrected by using the learnedvalue, thereby removing the sensor output error. For example, when thesensor output error is larger than a predetermined value that is setbeforehand, an output-error learning value (plus-side output error) iscalculated based on a sensor output after the PM forcible burning. Afterthe PM forcible burning, the accumulated PM on the insulating substrate32 is burned and removed, and thereby the PM accumulated amount=0, andVpm=0 V. However, if the sensor output error is caused, Vpm does notbecome zero (Vpm≠0 V). Thus, it is possible to calculate an output-errorlearning value based on the sensor output (i.e., PM detection voltageVpm) after the PM forcible burning.

The output-error learning value obtained after the PM forcible burningcorresponds to an output error after resetting the PM sensor 17 to aninitial state, and is referred to as “zero-point learning value”.

Furthermore, when the sensor output error is smaller than thepredetermined value that is set beforehand, an output-error learningvalue (minus-side output error) is calculated based on a sensor outputduring the PM forcible burning. The PM adhering to and accumulated onthe insulating substrate 32 has a temperature characteristic in whichthe resistance changes with respect to the temperature. For example, theresistance becomes smaller as the temperature becomes higher. During thePM forcible burning, because the resistance of the PM detector 34 isreduced, electrical current most easily flows between the detectionelectrodes 36 a, 36 b. In this case, the PM detection voltage Vpm isincreased to the output upper-limit value, and is held at the outputupper-limit value. However, if an output error is caused in the PMsensor 17, the PM detection voltage Vpm does not become the outputupper-limit value (Vpm≠output upper-limit value). Thus, it is possibleto calculate the output-error learning value during the PM forcibleburning, based on the sensor output (i.e., PM detection voltage Vpm). Inthe present embodiment, the output upper-limit value is about 5 V, forexample.

The output-error learning value obtained during the PM forcible burningcorresponds to an output error of the output upper-limit value of the PMsensor 17, and is referred to as “upper-limit learning value”.

Next, the learning of the output error will be described in detail. FIG.4 is a flow diagram showing a learning process of the sensor outputerror, which is repeatedly performed at a predetermined interval by themicrocomputer 44.

Referring to FIG. 4, at step S11, it is determined whether or not arequest for performing the forcible burning is made at the PM sensor 17.In this embodiment, a PM burning requirement flag is set by at lease oneof the start time of operation of the engine 11, the end time ofoperation of the engine 11, a time where the amount of accumulated PMreaches a predetermined amount, and a time period of operation of theengine 11 or a time where vehicle traveling distance after the previousPM forcible burning process reaches a predetermined value, so that theforcible burning requirement is output.

When the request for the forcible burning is not determined, theoperation proceeds to the step S12, without performing the PM forcibleburning process and the learning process of the PM sensor 17. At stepS12, the PM detection voltage Vpm is read as the detection signal of thePM sensor 17, and the PM detection voltage Vpm is corrected by using anoutput-error learning value. The output-error learning value is thezero-point learning value or the upper-limit learning value, calculatedin the previous learning process, and can be suitably read from theEEPROM 47. Next, at step S13, a corrected PM detection voltage Vpm iscalculated by using a map stored beforehand, and then the PM amountaccumulated on the insulating substrate 32 is calculated.

When the forcible burning request is determined, the operation proceedsto step S14 so as to perform the PM forcible burning operation at the PMsensor 17. Specifically, the energization of the heater 35 for the PMsensor 17 is turned on so as to heat the PM sensor 17. Thereafter, atstep 315, a burning execution counter is increased by 1.

A time delay is caused from when the heater 35 is turned on, to when theheater 35 becomes in a predetermined high-temperature state. That is,after a time passes from the heater 35 is turned on, the heater 35becomes in the predetermined high-temperature state. Thus, the heaterresistance is detected after the heater 35 is turned on, and thecounting-up of the burning execution counter is started after the heaterresistance reaches a predetermined value corresponding to thepredetermined high-temperature state of the heater 35.

Thereafter, at step S16, S17, the count value of the burning executioncounter is determined. That is, at step S16, it is determined whether ornot the counter value of the burning execution counter is equal to orlower than a first determination value K1. When the counter value of theburning execution counter is larger than the first determination valueK1 (i.e., the determination of Step S16 is NO), it is determined whetheror not the counter value of the burning execution counter reaches asecond determination value K2 that is larger than the firstdetermination value K1. That is, K1<K2. The first determination value K1is a threshold value for determining a time period from a start timingof the PM burning to a timing where the resistance value of the PMdetector 34 begins to decrease. More specifically, the firstdetermination value K1 is a threshold value for determining a timeperiod required that the PM detection voltage Vpm reaches the outputupper limit due to a decrease of the resistance of the PM detector 34,after the heater 35 is turned on. The second determination value K2 is athreshold value for determining whether a time period, required forfinishing the burning and removing of the PM accumulated on theinsulating substrate 32 due to the forcible burning, is elapsed.

When the counter value is equal to or lower than the first determinationvalue K1 at step S16, an upper-limit learning process is performed insteps S18 to S22. In contrast, when the counter value is equal to orlarger than the second determination value K2 at step S17, a zero-pointlearning process is performed in steps S23 to S27. When the countervalue is larger than the first determination value K1 and is smallerthan the second determination value K2, the control process istemporarily finished without performing the upper-limit learning processand the zero-point learning process.

When the upper-limit learning process is performed in a case where thecounter value≦K1, the PM detection voltage Vpm is calculated at stepS18, and it is determined whether the PM detection voltage Vpm is stablebased on the calculated and obtained PM detection voltage Vpm. Step S19determines whether the PM detection voltage Vpm is increased inaccordance with heater energization. When a variation amount of the PMdetection voltage Vpm is smaller than a predetermined value, it candetermine that the PM detection voltage Vpm is stable at step S19. Whenthe determination at step S19 is YES, it is determined whether the PMdetection voltage Vpm is equal to or larger than an abnormalitydetermination value KE1 at step S20. The abnormality determination valueKE1 is a threshold value for determining whether an abnormality iscaused in a case where the PM detection voltage Vpm is not increased toa predetermined voltage level in a previous burning period.

When the PM detection voltage Vpm is equal to or larger than KE1, anupper-time learning is performed at step S21. At this time, the presentPM detection voltage Vpm is made as an upper-limit learning value, andthe upper-limit learning value is stored in the EEPROM 47. The PMdetection voltage Vpm, after the YES determinations at step S19 and S20,corresponds to a second sensor standard value. In a time period wherethe PM detection voltage Vpm is stable, the PM detection voltage Vpm orthe mean value of the PM detection voltage Vpm may be calculated, andthe calculated value (second sensor standard value) may be adapted asthe upper-limit learning value. Alternatively, the values of Vpm withlarge variations may be not used in the calculation of the upper-limitlearning value, or a corrected value of the previous learning value witha limited variation may be adapted as the upper-limit learning value.

When the determination of step S20 is NO, it is determined that theoutput of the PM sensor 17 has an abnormality. At this time, anabnormality diagnosis data for indicating an output abnormality of thePM sensor 17 is stored in the EEPROM 47.

On the other hand, when the zero-point learning process is performed ina case where the counter value≧K2, the PM detection voltage Vpm iscalculated at step S23, and it is determined whether the PM detectionvoltage Vpm is stable based on the calculated and obtained PM detectionvoltage Vpm after the PM is burned and removed. Step S24 determineswhether the PM detection voltage Vpm is decreased and converges to about0 in accordance with the burning and removing of the PM. When avariation amount of the PM detection voltage Vpm is smaller than apredetermined value, it can determine that the PM detection voltage Vpmis stable at step S24. When the determination at step S24 is YES, it isdetermined whether the PM detection voltage Vpm is equal to or smallerthan an abnormality determination value KE2 at step S25. The abnormalitydetermination value KE2 is a threshold value for determining whether anabnormality is caused in a case where the PM detection voltage Vpm isnot decreased to a predetermined voltage level after the PM is burnedand removed.

When the PM detection voltage Vpm is equal to or smaller than KE2, thezero-point learning is performed at step S26. At this time, the presentPM detection voltage Vpm is made as a zero-point learning value, and thezero-point learning value is stored in the EEPROM 47. The PM detectionvoltage Vpm after the YES determinations at step S24 and S25 correspondsto a first sensor standard value. In a time period where the PMdetection voltage Vpm is stable, the PM detection voltage Vpm or themean value of the PM detection voltage Vpm may be calculated, and thecalculated value (first sensor standard value) may be adapted as thezero-point learning value. Alternatively, the values of Vpm with largevariations may be removed in the calculation of the upper-limit learningvalue, or a corrected value of the previous learning value with alimited variation may be adapted as the upper-limit learning value.

When the determination of step S25 is NO, it is determined whether theoutput of the PM sensor 17 has an abnormality. At this time, anabnormality diagnosis data for indicating an output abnormality of thePM sensor 17 is stored in the EEPROM 47.

FIG. 5 is a timechart for explaining the output error learning process.

Referring to FIG. 5, at the timing t1, a PM burning requirement flag isset to start the energization of the heater 35 at the PM sensor 17, soas to increase a heater resistance. Specifically, at the timing t1, thevalue of the burning execution counter is updated. After the timing t1,the temperature of the accumulated PM on the PM sensor 17 (insulatingsubstrate 32) increases so as to decrease the resistance between theelectrodes 36 a, 36 b, thereby increasing the PM detection voltage Vpm.

In the period from the timing t1 to the timing t2, the resistance (PMresistance) of the pair of electrodes 36 a, 36 b decreases in accordancewith a heating start of the heater 35, and thereby the PM detectionvoltage Vpm is increased to the output upper-limit value and is held atthe output upper-limit value. Thus, in the period from the timing t1 tothe timing t2, the upper-limit learning can be performed. The solid lineof the time chard regarding the Vpm indicates the normal values, in FIG.5. When the present PM detection voltage Vpm is smaller than the normalvalue as in the chain line of FIG. 5, the present PM detection voltageVpm is calculated as the upper-limit learning value. At the timing t2,the burning execution counter becomes equal to or larger than K1, andthe upper-limit learning is ended and the upper-limit learning end flagis set.

After the timing t2, the accumulated PM is burned and removed, so thatthe resistance (PM resistance) between the pair of the detectionelectrodes 36 a, 36 b is increased, and the PM detection voltage Vpm israpidly decreased to about 0 V. At the timing t3, the burning executioncounter reaches K2, and it is determined that the burning and removingof the PM is ended. At this time, the PM burning end flag is set, andthe zero-point learning is started. The solid line of the time chardregarding the Vpm indicates the normal value, in FIG. 5. When thepresent PM detection voltage Vpm is larger than the normal value as inthe chain line of FIG. 5 after the timing t2, the present PM detectionvoltage Vpm is calculated as the zero-point learning value. At thetiming t3, the zero-point learning is ended, and the zero-point learningend flag is set.

In FIG. 5, the upper-limit shift of the PM detection voltage Vpm and thezero-point shift thereof are indicated by the same time chart. However,actually, the upper-limit shift of the PM detection voltage Vpm and thezero-point shift thereof are not caused at the same time, and may berespectively caused. Furthermore, FIG. 5 shows a normal operation inwhich the PM detection voltage Vpm during the PM burning is equal to orlarger than KE1, and the PM detection voltage Vpm after the burning andremoving the PM is equal to or smaller than KE2.

At the timing t4, the heater 35 is turned off because of the end of aseries of forcible burning processes, and the PM burning requirementflag is reset.

FIGS. 6A, 6B, 7A and 7B are graphs showing sensor output corrections byusing output error learning values. FIGS. 6A and 6B show zero-pointlearning values in which the zero-point of the PM detection voltage isshifted to the positive side with respect to the normal value, and FIGS.7A and 7B show upper-limit learning values in which the upper-limit ofthe PM detection voltage is shifted to the negative side with respect tothe normal value. In the graphs of FIGS. 6A, 6B, 7A and 7B, the solidlines indicate the normal sensor output characteristics in which theoutput error is not caused, and the chain lines indicate the sensoroutput characteristics in which the sensor output error is caused.

The PM detection voltage Vpm is adapted as an example of the outputcharacteristics of the PM sensor 17. The PM detection voltage Vpmchanges in accordance with the PM accumulating amount on the PM detector34. In a case where the output error is not caused, the PM detectionvoltage Vpm becomes zero when the PM accumulating amount is zero, andthe PM detection voltage Vpm gradually increase as the PM accumulatingamount increases. Because the PM detection voltage Vpm is detected byusing the voltage-dividing circuit 40, the output characteristics of thePM detection voltage Vpm becomes in non-linear. For example, the PMdetection voltage Vpm is gradually approached to the voltage Vcc (5V) inaccordance with an increase of the PM accumulating amount, and becomesstable immediately before reaching the Vcc (5V).

Furthermore, the sensor output error may be caused such that the sensoroutput value (chain line graph) is larger than a predetermined normalvalue (solid line graph) as shown in FIGS. 5A and 6B. In this case, thePM detection voltage Vpm is corrected to be smaller with respect to thesensor output characteristic graph. As shown in the graph of FIG. 6A,the zero-point learning value is obtained in the zero-point learningprocess as a correction value ΔVpm1 of the Vpm, and the sensor outputcharacteristic is corrected by the correction amount so that thedetected Vpm is reduced by the same ratio with respect to the increaseof the PM accumulating amount, in the entire area of the PM accumulatingamount. That is, a different between the detected Vpm (chain-line graphin FIG. 6A) and the normal value (solid-line graph in FIG. 6A) is set asthe correction value ΔVpm1 that is increased by the same ratio as theincrease of the PM accumulating amount.

Alternatively, as shown in FIG. 6B, the correction value ΔVpm1 of theVpm may be calculated based on the zero-point learning value in a casewhere the PM accumulating amount is zero and in a case where the PMaccumulating amount is larger than zero, and then the correction of thesensor output characteristic may be performed in accordance with therespective correction values ΔVpm1 of the Vpm. For example, as shown inFIG. 6B, the zero-point learning value may be set as the correctionamount ΔVpm1 of the Vpm when the PM accumulating amount is zero. In thiscase, the correction amount ΔVpm1 of the Vpm may be set based onrespective PM accumulating amounts, such that the correction amountΔVpm1 of the Vpm becomes smaller as the PM accumulating amount islarger. That is, a different between the detected Vpm (chain-line graphin FIG. 6B) and the normal value (solid-line graph in FIG. 6B) is set asthe correction value ΔVpm1 that becomes smaller as the PM accumulatingamount becomes larger. Thus, the sensor output characteristic iscorrected so that the Vpm is reduced by the correction amount ΔVpm1, andthe correction amount ΔVpm1 is changed based on the PM accumulatingamount.

Furthermore, the sensor output error may be caused such that the sensoroutput value (chain line graph) is smaller than a predetermined normalvalue (solid line graph) as shown in FIGS. 7A and 7B. In this case, thePM detection voltage Vpm is corrected larger with respect to the sensoroutput characteristic. As shown in the graph of FIG. 7A, the upper-pointlearning value is obtained in the upper-point learning process as acorrection value ΔVpm2 of the Vpm, and the sensor output characteristicis corrected by the correction amount ΔVpm2 so that the detected Vpm isincreased by the same ratio with respect to an increase of the PMaccumulating amount, in the entire area of the PM accumulating amount.That is, a different between the detected Vpm (chain-line graph in FIG.7A) and the normal value (solid-line graph in FIG. 7A) is set as thecorrection value ΔVpm2 that is increased by the same ratio as theincrease of the PM accumulating amount.

Alternatively, as shown in FIG. 7B, the correction value ΔVpm2 of theVpm may be calculated based on the PM accumulating amount, and then thecorrection of the sensor output characteristic graph may be performed inaccordance with the correction value ΔVpm2 of the Vpm. For example, in astable area of the Vpm, the upper-limit learning value may be used asthe correction value ΔVpm2 of the Vpm, so that the correction amountΔVpm2 of the Vpm is made smaller as the PM accumulating amount becomessmaller, and the correction amount ΔVpm2 of the Vpm becomes zero whenthe PM accumulating amount is zero, as shown in FIG. 7B. Thus, thesensor output characteristic is corrected to be larger by the correctionamount ΔVpm2. As shown in FIG. 7B, the correction amount is increased asthe PM accumulating amount increases.

According to the present embodiment, the PM detection voltage Vpm iscalculated in a state where the PM is burned and removed from theinsulating substrate 32 as a first sensor standard value, based on thePM detection voltage Vpm obtained immediately after the burning andremoving of the PM, and is stored as the zero-point learning value.Thus, it is possible to determine an error even in a case where the PMdetection voltage Vpm after the burning and removing of the PM is not anordinary value when the PM accumulating amount is zero. Therefore,correction can be accurately performed with respect to the PM detectionvoltage Vpm. As a result, a detection error of the PM sensor 17 can beremoved, and the PM accumulating amount can be accurately detected byusing the PM sensor 17.

According to the present embodiment, the PM detection voltage Vpm iscalculated in a state where the resistance of the PM detector 34 isreduced based on the PM detection voltage Vpm during the burning of thePM, as a second sensor standard value, and is stored as the upper-limitlearning value. Thus, it is possible to determine a detection error evenin a case where the PM detection voltage Vpm during the PM burning isnot ordinary value (output upper limit). Therefore, the PM detectionvoltage Vpm can be suitably corrected.

According to the present embodiment, the upper-limit learning and thezero-point learning are performed. Therefore, the detection error of thePM sensor 17 can be effectively corrected in a case where the PMaccumulating amount is zero and in a case where the sensor output isaround the upper limit side.

In the present embodiment, the voltage-dividing circuit 40 is configuredby the PM detector 34 and the shunt resistor 42, such that the PMdetection voltage Vpm is output as a voltage at a middle point betweenthe PM detector 34 and the shunt resistor 42. Therefore, a detectionerror of the PM sensor 17, including a circuit error, can be effectivelyremoved.

In the present embodiment, the PM detection voltage Vpm is corrected byusing different correction amounts based on the zero-point learningvalue, in a case where the PM accumulating amount is zero and in a casewhere the PM accumulating amount is larger than zero. Thus, even whenthe PM detection voltage Vpm is corrected by using the zero-pointlearning value, the correction of the PM detection voltage Vpm can besuitably performed in a wide range of the PM accumulating amount.

Furthermore, the PM detection voltage Vpm can be corrected by usingdifferent correction values in accordance with the PM accumulatingamount based on the upper-limit learning value. Thus, even when the PMdetection voltage Vpm is corrected based on the upper-limit learningvalue, the correction of the PM detection voltage Vpm can be suitablyperformed in a wide range of the PM accumulating amount.

In the present embodiment, the diagnosis of abnormality is performedbased on the PM detection voltage Vpm obtained during the PM burning byusing the heating of the heater 35 or based on the PM detection voltageVpm obtained immediately after the burning and removing of the PM isfinished.

Then, after the heating of the heater 35 is started, the PM detectionvoltage Vpm is changed so that the resistance value of the PM detector34 is increased. Furthermore, the PM detection voltage Vpm obtainedwithin a predetermined change range is used as the zero-point learningvalue. Therefore, the zero-point learning value can be accuratelycalculated even in a case where the detection error of the PM sensor 17is caused and the PM detection voltage Vpm does not become zero.

After the heating of the heater 35 is started, the PM detection voltageVpm is changed so that the resistance value of the PM detector 34 isdecreased. Furthermore, the PM detection voltage Vpm obtained within apredetermined change range is used as the upper-limit learning value.Therefore, the upper-limit learning value can be accurately calculatedeven in a case where the detection error of the PM sensor 17 is causedand the PM detection voltage Vpm does not become the upper-limitlearning value.

Other Embodiments

The present invention is not limited to the contents disclosed in theabove embodiment, and may be applied as follows.

The upper limit learning value may be suitably calculated as follows.For example, in the PM forcible burning period, a maximum value Vmax ofthe PM detection voltage Vpm may be calculated by a peak holdprocessing, and the upper limit learning value can be calculated basedon the maximum value Vmax of the PM detection voltage Vpm. In this case,it can prevent the upper limit learning from being performed based onthe sensor output before the PM detection voltage Vpm reaches the outputupper-limit value or based on the sensor output after the PM detectionvoltage Vpm is reduced so as to increase the resistance value of the PMdetector 34. Thus, the correction of the sensor detection value can besuitably performed.

In the above embodiment, the voltage-dividing circuit 40 shown in FIG. 3is used as the signal output circuit. However, connection between the PMdetector 34 and the shunt resistor 42, for forming the voltage-dividingcircuit may be set reversely. Specifically, the PM detector 34 may beprovided on the lower side, and the shunt resistor 42 may be provided onthe higher side. In this arrangement, the PM detection voltage Vpm isdetermined by the following formula (2):Vpm=5 V×Rpm/(Rs+Rpm)  (2)

in which Rpm is a resistance of the PM detector 34, and Rs is aresistance (for example, 5 kΩ) of the shunt resistor 42.

In such a case, when the amount of accumulated PM is 0 (or about 0), theVpm is 5 V (Vpm=5V). The value of 5 V corresponds to the origin (0point). When the resistance Rpm of the PM detector 34 decreases to, forexample, 1 kΩ due to the accumulation of PM, the Vpm is 0.83 V(Vpm=0.83V). The range of a voltage of the voltage-dividing circuit 40is 0 to 5 V. The range of change in the PM detection voltage Vpm duringthe PM forcible burning is 0 to 0.83 V.

In the above described embodiment, a state immediately after the burningand removing of the PM may be determined and the zero-point learning maybe performed, when any one of the condition, where the burning executioncounter is equal to or larger than K2, and the condition, where the PMdetection voltage Vpm is stable after burning and removing the PM, issatisfied.

Furthermore, the upper-limit learning may be performed, when any one ofthe condition, where the burning execution counter is equal to orsmaller than K1, and the condition, where the PM detection voltage Vpmis stable after the PM detection voltage Vpm is increased due to thestart of the heater 35, is satisfied.

Furthermore, a heater resistance calculating means for calculating aheater resistance may be provided. In this case, a state during the PMburning or a state immediately after the burning and removing the PM maybe determined based on the calculated heater resistance, and thezero-point learning or the upper-limit learning may be performed. Theheater resistance calculating means detects a heater resistance voltageand a heater current when the heater 35 is turned on, and the heaterresistance value can be calculated based on the detected value. In thiscase, when the heater resistance is changed to be decreased after theheating of the PM due to the heater 35 is started, it is determined thatthe PM sensor 17 is in a state immediately after burning and removingthe PM. In this case, the PM detection voltage Vpm is obtained and thezero-point learning is performed. When the detection value of the heaterresistance is increased after the heating of the PM starts, it isdetermined that the PM sensor 17 is in the PM burning. In this case, thePM detection voltage Vpm may be obtained and the upper-limit learningmay be performed.

Alternatively, an electrical power amount consumed in the heater 35after being turned on may be calculated. In this case, a stateimmediately after burning and removing the PM may be determined based onthe consumed electrical power amount, and the zero-point learning may beperformed. Furthermore, a PM burning state may be determined based onthe consumed electrical power, and the upper-limit learning may beperformed in the PM burning state.

Alternatively, a sensor or the like for detecting a sensor elementtemperature or an exhaust gas temperature may be provided at adownstream side of the PM sensor 17 in the exhaust passage. In thiscase, a PM burning state may be determined based on the detectedtemperature of the sensor, and the upper-limit learning may be performedin the PM burning state. Furthermore, a state immediately after theburning and removing of the PM may be determined based on the detectedtemperature, and the zero-point learning may be performed. For example,when the detected temperature is increased or is higher than apredetermined temperature, it is determined that the PM sensor 17 is inthe PM burning state. In contrast, when the detected temperature isdecreased, it is determined that the PM sensor 17 is in a stateimmediately after the burning and removing of the PM.

In the present embodiment, the diagnosis of abnormality of the PM sensor17 is performed based on a variation amount of the PM detection voltageVpm obtained in the PM burning state or in a state immediately after theburning and removing the PM. At this time, when the variation amount ofthe PM detection voltage Vpm is equal to or larger than a determinationvalue, an abnormality can be determined.

In the above-described embodiment, the zero-point learning may beperformed regardless of whether the PM detection voltage Vpm is equal toor smaller than the abnormality determination value KE2. In this case,an abnormality diagnosis of the PM sensor 17 may be performed based onthe zero-point learning value obtained by the zero-point learningprocess. When the zero-point learning value is outside of apredetermined variation range, it is determined that the PM sensor 17has an abnormality.

In the above-described embodiment, the upper-limit learning may beperformed regardless of whether the PM detection voltage Vpm is equal toor larger than the abnormality determination value KE1. In this case, anabnormality diagnosis of the PM sensor 17 may be performed based on theupper-limit learning value obtained by the upper-limit learning process.When the upper-limit learning value is outside of a predeterminedvariation range, it is determined that the PM sensor 17 has anabnormality.

In the above embodiment, the heater 35 is provided in the insulatingsubstrate 32 of the PM sensor 17 as heating means for the PM forcibleburning. However, the heating means may be configured by using gas in anexhaust pipe, so that the temperature around the PM sensor 17 isincreased to a temperature at which the PM can be burned (for example,of 650° C.). In this case, the exhaust temperature can be increased byburning control of the engine, or an additional heater may be providedin the exhaust pipe.

The PM sensor 17 may be disposed on at least one of the downstream andupstream sides of a PM filter provided in an engine exhaust pipe andadapted for collecting PM. Further, based on a detected value of the PMsensor, the timing of reproducing the PM filter may be controlled.Alternatively, or additionally, based on the detected value of the PMsensor, the diagnosis of abnormality of the PM filter may be carriedout.

The sensor controller of above embodiment is applied to thedirect-injection gasoline engine, but can be applied to other types ofengines. For example, the sensor controller may be applied to a dieselengine (especially, a direct injection engine), and may be adapted tothe PM sensor provided in an exhaust pipe of the diesel engine. Theamount of PM contained in other kinds of gas except for the exhaust gasfrom the engine may be detected.

Although the present invention has been fully described in connectionwith the preferred embodiments thereof with reference to theaccompanying drawings, it is to be noted that various changes andmodifications will become apparent to those skilled in the art.

For example, according to an aspect of the above-described embodimentand modifications, a sensor controller is adapted to a particulatematter detection sensor 17. The particulate matter detection sensor 17includes an attachment portion (e.g., insulating substrate 32) to whichconductive particulate matter contained in gas is attached, and a pairof opposed electrodes (e.g., detection electrodes 36 a, 36 b) spacedfrom each other at the attachment portion. Furthermore, the particulatematter detection sensor 17 is adapted to output a detection signalcorresponding to a resistance between the pair of opposed electrodes.The sensor controller is adapted to calculate an amount of attachedparticulate matter based on a sensor detection value from theparticulate matter detection sensor 17. The sensor controller includes:a signal output circuit (e.g., voltage-dividing circuit 40) connected tothe particulate matter detection sensor 17 such that the sensordetection value is changeable in a predetermined output range by thesignal output circuit; a heater 35 configured to heat the attachmentportion so as to burn and remove the particulate matter attached to theattachment portion; learning means for obtaining the sensor detectionvalue in a burning of the particulate matter by using heat of the heater35, for calculating a sensor standard value in a state where theresistance between the pair of opposed electrodes is reduced based onthe obtained sensor detection value, and for storing the sensor standardvalue as a learning value; and correcting means for correcting thesensor detection value based on the sensor standard value stored by thelearning means. Here, the heater 35 may include a heating unit forburning and removing the particulate mater by using the heat generatedfrom the heater unit, and a heating means for heating the temperature ofexhaust gas to a burning temperature of the particulate matter.

Thus, even when the sensor standard value does not become a limit valuein the predetermined output range, an error of the particulate matterdetection sensor 17 can be determined, and the sensor detection valuecan be accurately corrected. As a result, a detection error of theparticulate matter detection sensor (PM sensor) 17 can be effectivelyreduced, and thereby the amount of particulate matter can be accuratelydetected.

For example, the signal output circuit may be a voltage-dividing circuit40 that has an electrode resistance corresponding to the resistance ofthe pair of opposed electrodes, a shunt resistance and an electricalsource portion. In this case, the voltage-dividing circuit may beconfigured to output a voltage at a middle point between the electroderesistance and the shunt resistance as the sensor detection value, andthe learning means may obtain the voltage at the middle point in theburning of the particulate matter and may calculate the sensor standardvalue based on the voltage at the middle point. Thus, the detectionerror including a circuit error can be accurately removed.

The correcting means may calculate correction values that are differentfrom each other in accordance with the amounts of the attachedparticulate matter based on the sensor standard value, and may correctthe sensor detection value by using the calculated correction values.Thus, even when the relationship between the attachment amount of theparticulate matter and the detected voltage is in a non-linecharacteristic, the sensor detection value can be accurately correctedin a wide range.

The sensor controller may include abnormality diagnosis means forperforming diagnosis of abnormality of the particulate matter detectionsensor based on the obtained sensor detection value. Furthermore, thelearning means may obtain the sensor detection value in a state wherethe resistance between the pair of opposed electrodes varies to bedecreased and a variation amount of the resistance is within apredetermined range, and may calculate the sensor standard value basedon the obtained sensor detection value.

For example, the correcting means calculates the correction value suchthat the correction value is smaller as the amount of the attachedparticulate matter becomes smaller and is larger as the amount of theattached particulate matter becomes larger. Furthermore, the sensorstandard value may be a threshold value for determining an elapsed timerequired for finishing the burning of the attached particulate matter.Alternatively, the sensor standard value may be a threshold value fordetermining an elapsed time from a timing where the heater is turned onto a timing where the burning of the attached particulate matter isstarted.

Such changes and modifications are to be understood as being within thescope of the present invention as defined by the appended claims.

What is claimed is:
 1. A controller for a particulate matter detectionsensor, the particulate matter detection sensor including an attachmentportion to which conductive particulate matter contained in gas isattached, and a pair of opposed electrodes spaced from each other at theattachment portion, the particulate matter detection sensor beingadapted to output a detection signal corresponding to a resistancebetween the pair of opposed electrodes, the controller being adapted tocalculate an amount of attached particulate matter based on a sensordetection value from the particulate matter detection sensor, thecontroller comprising: a signal output circuit connected to theparticulate matter detection sensor such that the sensor detection valueis changeable in a predetermined output range by the signal outputcircuit; a heater configured to heat the attachment portion so as toburn and remove the particulate matter attached to the attachmentportion; a learning portion for obtaining the sensor detection value ina burning of the particulate matter due to heating of the heater, forcalculating a sensor standard value in a state where the resistancebetween the pair of opposed electrodes is reduced based on the obtainedsensor detection value, and for storing the sensor standard value as alearning value; a correcting portion for correcting the sensor detectionvalue based on the sensor standard value stored by the learning portion,wherein: the sensor standard value is one of a zero-point learning valueand an upper-limit learning value; the correcting portion reduces thesensor detection value by a correction value calculated based on thezero-point learning value, and increases the sensor detection value by acorrection value calculated based on the upper-limit learning value; thecontroller further comprises a heater resistance calculating portioncalculating a heater resistance; the learning portion determines both astate during the burning of the particulate matter and a stateimmediately after the burning and removing the particulate matter basedon the calculated heater resistance, and executes both a zero-pointlearning and an upper-limit learning to calculate one of the zero-pointlearning value and the upper-limit learning value; and the controller isconfigured to: calculate an actual articulate matter amount based on thesensor detection value from the particulate matter detection sensor; andcontrol a state of an engine based on the actual particulate matteramount.
 2. The controller according to claim 1, wherein the signaloutput circuit is a voltage-dividing circuit that has an electroderesistance corresponding to the resistance of the pair of opposedelectrodes, a shunt resistance and an electrical source portion, thevoltage-dividing circuit is configured to output a voltage at a middlepoint between the electrode resistance and the shunt resistance as thesensor detection value, and the learning portion obtains the voltage atthe middle point in the burning of the particulate matter, andcalculates the sensor standard value based on the voltage at the middlepoint.
 3. The controller according to claim 1, wherein the correctingportion calculates correction values that are different from each otherin accordance with the amounts of the attached particulate matter basedon the sensor standard value, and corrects the sensor detection value byusing the calculated correction values.
 4. The controller according toclaim 1, further comprising an abnormality diagnosis portion forperforming diagnosis of abnormality of the particulate matter detectionsensor based on the obtained sensor detection value.
 5. The controlleraccording to claim 1, wherein the learning portion obtains the sensordetection value in a state where the resistance between the pair ofopposed electrodes varies to be decreased and a variation amount of theresistance is within a predetermined range, and calculates the sensorstandard value based on the obtained sensor detection value.
 6. Thecontroller according to claim 3, wherein the correcting portioncalculates the correction value such that the correction value issmaller as the amount of the attached particulate matter becomes smallerand is larger as the amount of the attached particulate matter becomeslarger.
 7. The controller according to claim 1, wherein the sensorstandard value is a threshold value for determining an elapsed timerequired for finishing the burning of the attached particulate matter.8. The controller according to claim 1, wherein the sensor standardvalue includes a first threshold value for determining an elapsed timefrom a timing where the heater is turned on to a timing where theburning of the attached particulate matter is started, and a secondthreshold value for determining an elapsed time required for finishingthe burning of the attached particulate matter.
 9. A controller for aparticulate matter detection sensor, the particulate matter detectionsensor including an attachment portion to which conductive particulatematter contained in gas is attached, and a pair of opposed electrodesspaced from each other at the attachment portion, the particulate matterdetection sensor being adapted to output a detection signalcorresponding to a resistance between the pair of opposed electrodes,the controller being adapted to calculate an amount of attachedparticulate matter based on a sensor detection value from theparticulate matter detection sensor, the controller comprising: a signaloutput circuit connected to the particulate matter detection sensor suchthat the sensor detection value is changeable in a predetermined outputrange by the signal output circuit; a heater configured to heat theattachment portion so as to burn and remove the particulate matterattached to the attachment portion; a processor configured to: obtainthe sensor detection value in a burning of the particulate matter due toheating of the heater; calculate a sensor standard value in a statewhere the resistance between the pair of opposed electrodes is reducedbased on the obtained sensor detection value; store the sensor standardvalue as a learning value; correct the sensor detection value based onthe stored sensor standard value, wherein the sensor standard value isone of a zero-point learning value and an upper-limit learning value;perform reduce the sensor detection value by a correction valuecalculated based on the zero-point learning value, and increase thesensor detection value by a correction value calculated based on theupper-limit learning value; calculate a heater resistance, wherein theprocessor is further configured to determine both a state during theburning of the particulate matter and a state immediately after theburning and removing the particulate matter based on the calculatedheater resistance and execute both a zero-point learning and anupper-limit learning to calculate one of the zero-point learning valueand the upper limit learning value; calculate an actual particulatematter amount based on the sensor detection value from the particulatematter detection sensor; and control a state of an engine based on theactual particulate matter amount.
 10. The controller according to claim9, wherein the signal output circuit is a voltage-dividing circuit thathas an electrode resistance corresponding to the resistance of the pairof opposed electrodes, a shunt resistance and an electrical sourceportion, the voltage-dividing circuit is configured to output a voltageat a middle point between the electrode resistance and the shuntresistance as the sensor detection value, and the processor is furtherconfigured to obtain the voltage at the middle point in the burning ofthe particulate matter, and calculate the sensor standard value based onthe voltage at the middle point.
 11. The controller according to claim9, wherein the processor is further configured to calculate correctionvalues that are different from each other in accordance with the amountsof the attached particulate matter based on the sensor standard value,and correct the sensor detection value by using the calculatedcorrection values.
 12. The controller according to claim 9, wherein theprocessor is further configured to perform diagnosis of abnormality ofthe particulate matter detection sensor based on the obtained sensordetection value.
 13. The controller according to claim 9, wherein theprocessor is further configured to obtain the sensor detection value ina state where the resistance between the pair of opposed electrodesvaries to be decreased and a variation amount of the resistance iswithin a predetermined range, and calculate the sensor standard valuebased on the obtained sensor detection value.
 14. The controlleraccording to claim 11, wherein the processor is further configured tocalculate the correction value such that the correction value is smalleras the amount of the attached particulate matter becomes smaller and islarger as the amount of the attached particulate matter becomes larger.15. The controller according to claim 9, wherein the sensor standardvalue is a threshold value for determining an elapsed time required forfinishing the burning of the attached particulate matter.
 16. Thecontroller according to claim 9, wherein the sensor standard valueincludes a first threshold value for determining an elapsed time from atiming where the heater is turned on to a timing where the burning ofthe attached particulate matter is started, and a second threshold valuefor determining an elapsed time required for finishing the burning ofthe attached particulate matter.